Machines such as dozers, loaders, excavators and other types of machinery typically include a hydro-mechanical power transmission system to transfer power, e.g., torque and rotational speed generated by a power source, to one or more connected loads, such as a machine tool or other implement. A major component of these hydro-mechanical power transmission systems is a hydraulic pump. The hydraulic pump or pumps generate pressurized hydraulic fluid that is used to operate the components of the machine.
One type of hydraulic pump is a side-by-side hydraulic piston pump that includes a pump housing defining a gear cavity housing a spur gear set and a pump cavity housing a pair of piston pumps. The piston pumps each include reciprocating pistons arranged within a pump barrel that is operably connected to a rotating shaft. The pistons within each pump extend outwardly from one end of the corresponding pump barrel and impinge on a swash plate. As the barrel and the pistons rotate and the swash plate remains stationary, the pistons reciprocate with a stroke length determined by the orientation of the swash plate, causing hydraulic fluid to be drawn into the pump barrel on the expansion strokes of the pistons and to be discharged from the pump barrel under pressure on the compression strokes. A drive shaft that is operatively coupled to and driven by an engine or other power source of the machine extends into the pump housing, with one of the spur gears, or a drive gear, and one of the piston pumps, or a drive pump, being mounted on the drive shaft for rotation therewith. A driven shaft is mounted for rotation within the pump housing, with the other spur gear of the set, or a driven gear, and the other piston pump, or a driven pump, mounted on the driven shaft for rotation therewith. The driven gear meshes with the drive gear so that the drive pump and the driven pump rotate in opposite directions when the power source drives the drive shaft.
The pump housing is filled with lubricating fluid which surrounds the gear set, the piston pumps and the shafts. The pump cavity surrounds the piston pumps and provides space for the lubricating fluid to flow around and with each pump barrel as the piston pumps are turned by the gears. The drive pump turns in the direction that the drive shaft is driven, while the driven pump turns in the opposite direction. As the pump barrels turn, the surrounding lubricating fluid flows with the rotating pump barrels and pistons within the pump cavity in the direction of rotation of the pump barrels. As the lubricating fluid flowing in opposite directions around the pump barrel and the pistons meets in the area between the piston pumps, the lubricating fluid is churned by the rotating piston pumps due to the limited space between the piston pumps. The churning fluid results in power loss due to liquid resistance between the lubricating fluid and the surfaces of the pump barrels and pistons. The liquid resistance represents a parasitic load on the machine power source and can result in a power loss and decreased efficiency. For example, the power loss can be on the order of 0.4 kW in a 120 cc hydraulic pump.
In view of this, a need exists for an improved SBS piston pump housing assembly providing improved lubricant flow within the pump cavity with reduced parasitic power loss from churning of lubricating fluids within the housing assembly.